Field:
The present invention relates to an oral end tidal carbon dioxide probe.
Description of the Related Art:
Pulmonary embolism (PE) remains a diagnostic challenge and many studies are performed with a low yield at substantial financial cost and potential risk from radiation. End tidal carbon dioxide (EtCO2) is a surrogate for pulmonary vascular obstruction and subsequent dead space ventilation. Using EtCO2 as an initial screening test in patients being evaluated for PE would potentially spare many unnecessary, low-yield diagnostic studies and their associated risk and financial burden.
Pulmonary embolism (PE) is a common concern in the evaluation of diverse clinical presentations including chest pain, dyspnea and hypoxemia. Extensive diagnostic evaluation, including contrast enhanced helical computed tomography (CT), is frequently undertaken, despite a relatively low incidence of disease [2]. In addition to the cost of these studies, the risks of contrast and radiation exposure add to the burden of evaluation [3, 4]. Throughout this Specification, the numeral(s) inside of brackets refers to a literature citation. The list of literature cited appears at the end of the Detailed Description.
Diagnostic algorithms to simplify testing procedures in PE diagnosis have been explored, most combining D-dimer testing and CT angiography [5, 6]. D-dimer testing requires venipuncture and time for test performance. [1, 5] CT angiography use in PE diagnosis has increased markedly [2]. As a low percentage of CT angiograms demonstrate PE [2, 7, 8], concern has been raised of the contrast and radiation risk [4, 9]. Clinical prediction rules, including the Wells score, have also been proposed [6, 10] which have the advantage of instantaneous results, avoidance of invasive procedures, and low risk and cost.
With rising numbers of patients being evaluated for PH and the substantial cost, time, and potential risk in evaluation of pulmonary vascular disease [48], there is an interest in developing new, non-invasive diagnostic techniques to identify patients at low risk for PAH. Currently, final confirmation of diagnosis of PAH requires RHC, in part, to rule out PVH. While there are clinical and echocardiographic features that may make PVH more likely [31, 43], these indicators are often not adequately compelling to dissuade clinicians from pursuing RHC in patients with elevated right ventricular systolic pressure on echocardiography or evidence of cor pulmonale. Alternatively, clinicians may treat presumptive PAH with expensive and potentially harmful medications based on clinical and echocardiographic findings. Although cardiopulmonary exercise testing reveals differences in exhaled CO2 and ventilatory efficiency between patients with PAH and PVH [34, 38], this test is not available at the bedside, the required expertise is not found at some institutions, and has limitations in non-ambulatory patients.
Distinguishing pulmonary arterial hypertension (PAH) from other forms of pulmonary hypertension (PH) such as pulmonary venous hypertension (PVH) can be difficult at the bedside, even with use of echocardiography or other non-invasive techniques. While recent reports have suggested a potential role for analysis of “notch” pattern in right ventricular outflow tract Doppler flow velocity, right heart catheterization (RHC) with provocative procedures is usually required for accurate distinction of PAH from PVH associated with non-systolic heart failure [28-31]. This distinction is crucial as therapies for these two conditions and prognoses are different. Moreover, determining response to therapy in PAH is challenging with many well-described limitations of standard non-invasive six minute walk test (6MWT) [30, 32], and logistic challenges and expense with frequent RHC. Thus, there is a need for efficient, non-invasive testing of PE and distinguishing PAH from PVH and determining response to therapy in PAH is needed. A non-invasive, bedside test with good negative predictive value for PAH is a much needed diagnostic tool.